1. Field of the Invention
The present invention relates to a stepping motor drive apparatus and to a stepping motor that are applied to a technical field in which high accuracy, high torque output, and high speed are required, such as in optical disk drives, printers, copying machines, robots, machine tools, and the like, and more specifically to a stepping motor drive apparatus and stepping motor that detect the position of a rotor so that close-loop control is performed.
2. Description of Related Art
A stepping motor having a plurality of excitation phases is generally driven by shifting the phase for each excitation phase with respect to number of phases as used and exciting each phase sequentially.
However, there are cases, depending upon specifications such as the rotational position accuracy of the equipment into which the stepping motor is built, in which a positioning accuracy greater than the intrinsic positioning accuracy of the stepping motor and a higher torque are required.
In such cases, the microstep driving method and method of performing closed-loop control with detecting the position of the rotor have been used in the past.
The microstep driving method is the generally used method that is one of driving the motor with a step that is smaller than the usual step, and an driver IC for this microstep driving method has already been made commercially available.
In contrast to this, the closed-loop control method of detecting the rotor position has been disclosed, for example, in the Japanese Unexamined Patent Publication (KOKAI) No. 61-88796 and No. 62-244264.
In the Japanese Unexamined Patent Publication (KOKAI) No. 61-88796, there is disclosure of sensor position detection apparatus which has a phase switcher which arbitrarily controls the switching of the excitation phases of a rotating-type or linear-type stepping motor, a position signal generation means which outputs an arbitrary signal having a period that is the same as the period of the balance point of each excitation phase, a timer which measures the time from the time at which an arbitrary excitation phase is excited in accordance with the control of the phase switcher, until the time at which the position detection signal output by the position signal generation means is detected, and a sensor position calculator which calculates, by means of the time measured by the timer, the distance between the excitation phase balance point and the detection point of the position signal generation means.
According to this sensor position detection apparatus, the timer is used to measure the amount of time required for the rotor to move from the balance point to the position signal detection point when the stepping motor is moves 1 step to the right or to the left and, based on this, the positional relationship between the motor balance point and the sensor detection point is determined, thereby having the effect of eliminating the need to perform positioning of the sensor detection point and the motor balance point.
In the Japanese Unexamined Patent Publication (KOKAI) No. 62-244264, there is disclosure of a motor drive apparatus in which the magnetic flux of a rotor, which is formed by a permanent magnet, is detected by a position detection element in order to perform control of the rotation of the rotor, wherein a magnet which is magnetized in the same manner as the rotor is fixed to the end surface of the rotor, and further wherein a position detection element is disposed in opposition to this magnet.
In this motor drive apparatus, a Hall element is used as the means to detect the rotational position of the rotor of the motor. The rotor of the motor is the same type of magnet as the stepping motor, the position being detected by the Hall element and the excitation being switched.
In consideration of the deterioration of the signal in this motor drive apparatus when a rotor magnet is used for detection of the magnetic flux by a Hall element, a separate magnet having the same magnetic poles with respect to the rotation direction is provided.
By doing this, signal quality deterioration is prevented. In this motor drive apparatus, the current value when current is driven through the coil of each of the phases is constant, this being used in applications with constant rotational speed.
In addition, the "position detection apparatus" of Japanese Unexamined Patent Publication (KOKAI) No. 6-323806, the "brushless DC motor drive apparatus" of Japanese Unexamined Patent Publication (KOKAI) No. 4-222491. and the "AC motor magnetic sensor" of Japanese Unexamined Utility Model Publication (KOKAI) No. 6-12906, for example, disclose examples of using a Hall element as a sensor for excitation switching in a DC brushless motor or AC motor.
In the above-described microstep drive method, because drive is done by a fine step, there is the problem that the rotational force becomes small and the torque characteristics deteriorate.
Additionally, because the resolution is finite, there is also a limit to positioning accuracy. While a method of increasing the resolution of the microstep method could be envisioned, the stepping motor excitation pattern is dependent on the intrinsic motor characteristics, and there is a limit to the improvement in resolution.
The "sensor position detection apparatus" disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 61-88796 detects the stepping motor rotor position and optimizes the excitation timing and, while this is effective in the case of driving a motor at a prescribed target speed, it is cannot be claimed to be particularly effective in the case of positioning the rotor by causing it to stop at a prescribed rotational position.
With a stepping motor of a closed-loop system in the past, a high-cost sensor, such as a rotary encoder or optical sensor or the like, was used at the sensor to detect the rotor position, this creating the problem of high equipment cost.
Because the "motor drive apparatus" that is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 62-244264 has another permanent magnet that is magnetized with a number of poles that is the same as the rotor fixed to the end surface of the rotor, which is a permanent magnet, there is the problem of a complex construction.
Additionally, in the examples of the past which are disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 6-323806 and No. 4-222491 and in the Japanese Unexamined Utility Model Publication (KOKAI) No. 6-12906, the detection signals that are output from a Hall element are all converted to pulses for drive of the motor.
However, because a Hall element is disposed so as to be in proximity to the rotor, interference occurs because of the magnetic field of the coil, the influence of this interference resulting in a larger time skew when the analog signal is converted to a pulse signal. As a result, it is not possible to perform proper motor drive and, in certain cases, faulty operation can occur.
The present invention was made to solve the above-noted problems, and has as an object the provision of a low-cost stepping motor drive apparatus and stepping motor that provides high accuracy and high torque output.